On the display panels of portable personal digital assistants and cell phones, some display information characteristics, e.g. residual owner, signal icons instead of array type display panels show intensity, call ringing and envelope. Therefore, a low-resolution problem caused by array type display panels is solved.
Referring to FIG. 1A, it is a cross-sectional view of a conventional structure using an organic EL element to form a pattern on the display panel. FIG. 1B is a top view of a first display electrode.
As shown in FIG. 1A, the organic EL element includes a first display electrode 22, i.e. an Indium-tin Oxide (ITO) film, formed on a substrate 21 which is composed of light-transparent glass. A pattern of the first electrode 22 formed by etching the ITO film is shown in FIG. 1B. An organic function layer 23, including a stacked structure of a hole injection layer, a hole transport layer, an emitting layer, an electron transport layer and an electron injection layer, and a second display electrode 24 are layered in turn on the substrate 21 and first display electrode 22. When a specific voltage is applied to the first and second display electrodes 22 and 24, a current flows through an area of the organic function layer 23 between electrodes 22 and 24, the light-emitting area of organic function layer 23 emits a corresponding pattern of an icon showed in FIG. 1B.
Such pattern of the icon, which comes from an organic EL element by utilizing the above method is defined by a first display electrode 22. However, the first display electrode 22 and the substrate 21 are made of different materials, so that their reflectivities, transmissivities and refractive indexes are not equivalent. Then, the defects of the pattern of an icon are visible from the side of the substrate 21 while no voltage is applied between these electrodes.
To improve the above disadvantages, U.S. Pat. No. 5,949,186 of Pioneer Electronic Corporation, entitled “organic electroluminescent element” (issued date, Sep. 7, 1999) shows a structure using the organic EL element to manufacture icons in a display panel.
Referring to FIG. 2A, it is a cross-sectional view of a conventional structure using the organic EL element to form a pattern on the display panel. FIG. 2B is a top view of an electron injection layer.
As shown in FIG. 2A, the organic EL element includes a first display electrode 32, i.e. an ITO film, formed on a substrate 31. An organic function layer is layered on the first display electrode 32. The organic function layer includes an electron injection layer 34 having a pattern shown in FIG. 2B, and a combined layer 33 composed of a hole injection, a hole transport layer, an emitting layer, and an electron transport layer. A second display electrode 35 is thereafter formed on the organic layers. When a specific voltage is applied to the first and second electrodes 32 and 35, a current flows through only an area of the organic function layer, which is defined by an electron injection layer 34, and the light-emitting area creates a corresponding pattern of an icon shown in FIG. 2B.
Referring to FIG. 3A, it is a cross-sectional view of a conventional structure using the organic EL element to form a pattern on the display panel. FIG. 3B is a top view of a hole injection layer.
As shown in FIG. 3A, the organic EL element includes a first display electrode 42, i.e. an ITO film, formed on substrate 41. An organic function layer is layered on the first display electrode 42. The organic function layer includes a hole injection layer 48 having a pattern shown in FIG. 3B, and a combined layer 49 composed of a hole transport layer 48, an emitting layer, an electron transport layer, and an electron injection layer. A second display electrode 40 is layered on the organic function layer. When a specific voltage is applied to the first and second electrodes 42 and 40, a current flows through only an area of the organic function layer, which is defined by the hole injection layer 48, and the light-emitting area generates a corresponding pattern of an icon shown in FIG. 3B.
Referring to FIG. 4A, it is a cross-sectional view of a structure of a conventional method using the organic EL element to form a pattern on the display panel. FIG. 4B is a top view of an electron obstruction layer.
As shown in FIG. 4A, the organic EL element includes a first display electrode 50, i.e. an ITO film, formed on substrate 59. An organic function layer 51 is layered on the first display electrode 50. An electron obstruction layer 52 having a pattern, shown in FIG. 4B, is formed on the organic function layer 51. Then, a second display electrode 53 is layered both on the organic function layer and the electron obstruction layer. When a specific voltage is applied to the first and second electrodes 50 and 53, a current flows through only an area of the organic function layer, which is not determined by the electron obstruction layer 52, and the light-emitting area produces, a corresponding pattern 57 of an icon shown in FIG. 4B.
Referring to FIG. 5A, it is a cross-sectional view of a structure of a conventional method using the organic EL element to form a pattern on the display panel. FIG. 5B is a top view of a hole obstruction layer.
As shown in FIG. 5A, the organic EL element includes a first display electrode 62, i.e. an ITO film, formed on substrate 61. A hole injection layer 67 covered with the organic function layer is layered on the first display electrode 62. A hole obstruction layer having a pattern shown in FIG. 5B is formed on the hole injection layer. Then, a combined layer 69 stacked with a hole transport layer, an emitting layer, an electron transport layer and an electron injection layer, and the second display electrode 66 are layered on the hole injection layer and the hole obstruction layer. When a specific voltage is applied to the first and second electrodes 62 and 66, a current flows through only an area of the organic functioning layer, which is not determined by the hole obstruction layer 52, and the light-emitting area brings a corresponding pattern 63 of an icon shown in FIG. 5B.
The organic EL element shown by Pioneer Electronic Corporation uses the ITO film as the continuous surface. However, during the process of manufacturing patterns on an electron injection layer, a hole injection layer, an electron obstruction layer or hole obstruction layer, the formation of patterns is utilizing metal mask process for evaporation that increase the complex as well as the disadvantages of pollution and vulnerable pattern control. In addition, the metal mask processes are not compatible with the conventional method of manufacturing an array type display panel. So the processes of the array type display panel and the organic EL element must be divided, and it increases the complexity of manufacturing the display panel.